#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"

#ifdef QUANT_2PASS_SUPPORTED


/*
   This module implements the well-known Heckbert paradigm for color
   quantization.  Most of the ideas used here can be traced back to
   Heckbert's seminal paper
     Heckbert, Paul.  "Color Image Quantization for Frame Buffer Display",
     Proc. SIGGRAPH '82, Computer Graphics v.16 #3 (July 1982), pp 297-304.

   In the first pass over the image, we accumulate a histogram showing the
   usage count of each possible color.  To keep the histogram to a reasonable
   size, we reduce the precision of the input; typical practice is to retain
   5 or 6 bits per color, so that 8 or 4 different input values are counted
   in the same histogram cell.

   Next, the color-selection step begins with a box representing the whole
   color space, and repeatedly splits the "largest" remaining box until we
   have as many boxes as desired colors.  Then the mean color in each
   remaining box becomes one of the possible output colors.

   The second pass over the image maps each input pixel to the closest output
   color (optionally after applying a Floyd-Steinberg dithering correction).
   This mapping is logically trivial, but making it go fast enough requires
   considerable care.

   Heckbert-style quantizers vary a good deal in their policies for choosing
   the "largest" box and deciding where to cut it.  The particular policies
   used here have proved out well in experimental comparisons, but better ones
   may yet be found.

   In earlier versions of the IJG code, this module quantized in YCbCr color
   space, processing the raw upsampled data without a color conversion step.
   This allowed the color conversion math to be done only once per colormap
   entry, not once per pixel.  However, that optimization precluded other
   useful optimizations (such as merging color conversion with upsampling)
   and it also interfered with desired capabilities such as quantizing to an
   externally-supplied colormap.  We have therefore abandoned that approach.
   The present code works in the post-conversion color space, typically RGB.

   To improve the visual quality of the results, we actually work in scaled
   RGB space, giving G distances more weight than R, and R in turn more than
   B.  To do everything in integer math, we must use integer scale factors.
   The 2/3/1 scale factors used here correspond loosely to the relative
   weights of the colors in the NTSC grayscale equation.
   If you want to use this code to quantize a non-RGB color space, you'll
   probably need to change these scale factors.
*/

#define R_SCALE 2		/* scale R distances by this much */
#define G_SCALE 3		/* scale G distances by this much */
#define B_SCALE 1		/* and B by this much */

/* Relabel R/G/B as components 0/1/2, respecting the RGB ordering defined
   in jmorecfg.h.  As the code stands, it will do the right thing for R,G,B
   and B,G,R orders.  If you define some other weird order in jmorecfg.h,
   you'll get compile errors until you extend this logic.  In that case
   you'll probably want to tweak the histogram sizes too.
*/

#if RGB_RED == 0
#define C0_SCALE R_SCALE
#endif
#if RGB_BLUE == 0
#define C0_SCALE B_SCALE
#endif
#if RGB_GREEN == 1
#define C1_SCALE G_SCALE
#endif
#if RGB_RED == 2
#define C2_SCALE R_SCALE
#endif
#if RGB_BLUE == 2
#define C2_SCALE B_SCALE
#endif


/*
   First we have the histogram data structure and routines for creating it.

   The number of bits of precision can be adjusted by changing these symbols.
   We recommend keeping 6 bits for G and 5 each for R and B.
   If you have plenty of memory and cycles, 6 bits all around gives marginally
   better results; if you are short of memory, 5 bits all around will save
   some space but degrade the results.
   To maintain a fully accurate histogram, we'd need to allocate a "long"
   (preferably unsigned long) for each cell.  In practice this is overkill;
   we can get by with 16 bits per cell.  Few of the cell counts will overflow,
   and clamping those that do overflow to the maximum value will give close-
   enough results.  This reduces the recommended histogram size from 256Kb
   to 128Kb, which is a useful savings on PC-class machines.
   (In the second pass the histogram space is re-used for pixel mapping data;
   in that capacity, each cell must be able to store zero to the number of
   desired colors.  16 bits/cell is plenty for that too.)
   Since the JPEG code is intended to run in small memory model on 80x86
   machines, we can't just allocate the histogram in one chunk.  Instead
   of a true 3-D array, we use a row of pointers to 2-D arrays.  Each
   pointer corresponds to a C0 value (typically 2^5 = 32 pointers) and
   each 2-D array has 2^6*2^5 = 2048 or 2^6*2^6 = 4096 entries.  Note that
   on 80x86 machines, the pointer row is in near memory but the actual
   arrays are in far memory (same arrangement as we use for image arrays).
*/

#define MAXNUMCOLORS  (MAXJSAMPLE+1) /* maximum size of colormap */

/* These will do the right thing for either R,G,B or B,G,R color order,
   but you may not like the results for other color orders.
*/
#define HIST_C0_BITS  5		/* bits of precision in R/B histogram */
#define HIST_C1_BITS  6		/* bits of precision in G histogram */
#define HIST_C2_BITS  5		/* bits of precision in B/R histogram */

/* Number of elements along histogram axes. */
#define HIST_C0_ELEMS  (1<<HIST_C0_BITS)
#define HIST_C1_ELEMS  (1<<HIST_C1_BITS)
#define HIST_C2_ELEMS  (1<<HIST_C2_BITS)

/* These are the amounts to shift an input value to get a histogram index. */
#define C0_SHIFT  (BITS_IN_JSAMPLE-HIST_C0_BITS)
#define C1_SHIFT  (BITS_IN_JSAMPLE-HIST_C1_BITS)
#define C2_SHIFT  (BITS_IN_JSAMPLE-HIST_C2_BITS)


typedef UINT16 histcell;	/* histogram cell; prefer an unsigned type */

typedef histcell FAR * histptr;	/* for pointers to histogram cells */

typedef histcell hist1d[HIST_C2_ELEMS]; /* typedefs for the array */
typedef hist1d FAR * hist2d;	/* type for the 2nd-level pointers */
typedef hist2d * hist3d;	/* type for top-level pointer */


/* Declarations for Floyd-Steinberg dithering.

   Errors are accumulated into the array fserrors[], at a resolution of
   1/16th of a pixel count.  The error at a given pixel is propagated
   to its not-yet-processed neighbors using the standard F-S fractions,
 		...	(here)	7/16
 		3/16	5/16	1/16
   We work left-to-right on even rows, right-to-left on odd rows.

   We can get away with a single array (holding one row's worth of errors)
   by using it to store the current row's errors at pixel columns not yet
   processed, but the next row's errors at columns already processed.  We
   need only a few extra variables to hold the errors immediately around the
   current column.  (If we are lucky, those variables are in registers, but
   even if not, they're probably cheaper to access than array elements are.)

   The fserrors[] array has (#columns + 2) entries; the extra entry at
   each end saves us from special-casing the first and last pixels.
   Each entry is three values long, one value for each color component.

   Note: on a wide image, we might not have enough room in a PC's near data
   segment to hold the error array; so it is allocated with alloc_large.
*/

#if BITS_IN_JSAMPLE == 8
typedef INT16 FSERROR;		/* 16 bits should be enough */
typedef int LOCFSERROR;		/* use 'int' for calculation temps */
#else
typedef JPEG_INT32 FSERROR;		/* may need more than 16 bits */
typedef JPEG_INT32 LOCFSERROR;	/* be sure calculation temps are big enough */
#endif

typedef FSERROR FAR *FSERRPTR;	/* pointer to error array (in FAR storage!) */


/* Private subobject */

typedef struct {
  struct jpeg_color_quantizer pub; /* public fields */

  /* Space for the eventually created colormap is stashed here */
  JSAMPARRAY sv_colormap;	/* colormap allocated at init time */
  int desired;			/* desired # of colors = size of colormap */

  /* Variables for accumulating image statistics */
  hist3d histogram;		/* pointer to the histogram */

  wxjpeg_boolean needs_zeroed;		/* TRUE if next pass must zero histogram */

  /* Variables for Floyd-Steinberg dithering */
  FSERRPTR fserrors;		/* accumulated errors */
  wxjpeg_boolean on_odd_row;		/* flag to remember which row we are on */
  int * error_limiter;		/* table for clamping the applied error */
} my_cquantizer;

typedef my_cquantizer * my_cquantize_ptr;


/*
   Prescan some rows of pixels.
   In this module the prescan simply updates the histogram, which has been
   initialized to zeroes by start_pass.
   An output_buf parameter is required by the method signature, but no data
   is actually output (in fact the buffer controller is probably passing a
   NULL pointer).
*/

METHODDEF( void )
prescan_quantize( j_decompress_ptr cinfo, JSAMPARRAY input_buf,
                  JSAMPARRAY output_buf, int num_rows ) {
  my_cquantize_ptr cquantize = ( my_cquantize_ptr ) cinfo->cquantize;
  register JSAMPROW ptr;
  register histptr histp;
  register hist3d histogram = cquantize->histogram;
  int row;
  JDIMENSION col;
  JDIMENSION width = cinfo->output_width;
  for( row = 0; row < num_rows; row++ ) {
    ptr = input_buf[row];
    for( col = width; col > 0; col-- ) {
      /* get pixel value and index into the histogram */
      histp = & histogram[GETJSAMPLE( ptr[0] ) >> C0_SHIFT]
              [GETJSAMPLE( ptr[1] ) >> C1_SHIFT]
              [GETJSAMPLE( ptr[2] ) >> C2_SHIFT];
      /* increment, check for overflow and undo increment if so. */
      if( ++( *histp ) <= 0 )
      { ( *histp )--; }
      ptr += 3;
    }
  }
}


/*
   Next we have the really interesting routines: selection of a colormap
   given the completed histogram.
   These routines work with a list of "boxes", each representing a rectangular
   subset of the input color space (to histogram precision).
*/

typedef struct {
  /* The bounds of the box (inclusive); expressed as histogram indexes */
  int c0min, c0max;
  int c1min, c1max;
  int c2min, c2max;
  /* The volume (actually 2-norm) of the box */
  JPEG_INT32 volume;
  /* The number of nonzero histogram cells within this box */
  long colorcount;
} box;

typedef box * boxptr;

static boxptr find_biggest_color_pop( boxptr boxlist, int numboxes ) {
  register boxptr boxp;
  register int i;
  register long maxc = 0;
  boxptr which = NULL;
  for( i = 0, boxp = boxlist; i < numboxes; i++, boxp++ ) {
    if( boxp->colorcount > maxc && boxp->volume > 0 ) {
      which = boxp;
      maxc = boxp->colorcount;
    }
  }
  return which;
}

static boxptr find_biggest_volume( boxptr boxlist, int numboxes ) {
  register boxptr boxp;
  register int i;
  register JPEG_INT32 maxv = 0;
  boxptr which = NULL;
  for( i = 0, boxp = boxlist; i < numboxes; i++, boxp++ ) {
    if( boxp->volume > maxv ) {
      which = boxp;
      maxv = boxp->volume;
    }
  }
  return which;
}

static void update_box( j_decompress_ptr cinfo, boxptr boxp ) {
  my_cquantize_ptr cquantize = ( my_cquantize_ptr ) cinfo->cquantize;
  hist3d histogram = cquantize->histogram;
  histptr histp;
  int c0, c1, c2;
  int c0min, c0max, c1min, c1max, c2min, c2max;
  JPEG_INT32 dist0, dist1, dist2;
  long ccount;
  c0min = boxp->c0min;
  c0max = boxp->c0max;
  c1min = boxp->c1min;
  c1max = boxp->c1max;
  c2min = boxp->c2min;
  c2max = boxp->c2max;
  if( c0max > c0min )
    for( c0 = c0min; c0 <= c0max; c0++ )
      for( c1 = c1min; c1 <= c1max; c1++ ) {
        histp = & histogram[c0][c1][c2min];
        for( c2 = c2min; c2 <= c2max; c2++ )
          if( *histp++ != 0 ) {
            boxp->c0min = c0min = c0;
            goto have_c0min;
          }
      }
have_c0min:
  if( c0max > c0min )
    for( c0 = c0max; c0 >= c0min; c0-- )
      for( c1 = c1min; c1 <= c1max; c1++ ) {
        histp = & histogram[c0][c1][c2min];
        for( c2 = c2min; c2 <= c2max; c2++ )
          if( *histp++ != 0 ) {
            boxp->c0max = c0max = c0;
            goto have_c0max;
          }
      }
have_c0max:
  if( c1max > c1min )
    for( c1 = c1min; c1 <= c1max; c1++ )
      for( c0 = c0min; c0 <= c0max; c0++ ) {
        histp = & histogram[c0][c1][c2min];
        for( c2 = c2min; c2 <= c2max; c2++ )
          if( *histp++ != 0 ) {
            boxp->c1min = c1min = c1;
            goto have_c1min;
          }
      }
have_c1min:
  if( c1max > c1min )
    for( c1 = c1max; c1 >= c1min; c1-- )
      for( c0 = c0min; c0 <= c0max; c0++ ) {
        histp = & histogram[c0][c1][c2min];
        for( c2 = c2min; c2 <= c2max; c2++ )
          if( *histp++ != 0 ) {
            boxp->c1max = c1max = c1;
            goto have_c1max;
          }
      }
have_c1max:
  if( c2max > c2min )
    for( c2 = c2min; c2 <= c2max; c2++ )
      for( c0 = c0min; c0 <= c0max; c0++ ) {
        histp = & histogram[c0][c1min][c2];
        for( c1 = c1min; c1 <= c1max; c1++, histp += HIST_C2_ELEMS )
          if( *histp != 0 ) {
            boxp->c2min = c2min = c2;
            goto have_c2min;
          }
      }
have_c2min:
  if( c2max > c2min )
    for( c2 = c2max; c2 >= c2min; c2-- )
      for( c0 = c0min; c0 <= c0max; c0++ ) {
        histp = & histogram[c0][c1min][c2];
        for( c1 = c1min; c1 <= c1max; c1++, histp += HIST_C2_ELEMS )
          if( *histp != 0 ) {
            boxp->c2max = c2max = c2;
            goto have_c2max;
          }
      }
have_c2max:
  dist0 = ( ( c0max - c0min ) << C0_SHIFT ) * C0_SCALE;
  dist1 = ( ( c1max - c1min ) << C1_SHIFT ) * C1_SCALE;
  dist2 = ( ( c2max - c2min ) << C2_SHIFT ) * C2_SCALE;
  boxp->volume = dist0 * dist0 + dist1 * dist1 + dist2 * dist2;
  /* Now scan remaining volume of box and compute population */
  ccount = 0;
  for( c0 = c0min; c0 <= c0max; c0++ )
    for( c1 = c1min; c1 <= c1max; c1++ ) {
      histp = & histogram[c0][c1][c2min];
      for( c2 = c2min; c2 <= c2max; c2++, histp++ )
        if( *histp != 0 ) {
          ccount++;
        }
    }
  boxp->colorcount = ccount;
}


static int median_cut( j_decompress_ptr cinfo, boxptr boxlist, int numboxes,
                       int desired_colors )
/* Repeatedly select and split the largest box until we have enough boxes */
{
  int n, lb;
  int c0, c1, c2, cmax;
  register boxptr b1, b2;
  while( numboxes < desired_colors ) {
    /* Select box to split.
       Current algorithm: by population for first half, then by volume.
    */
    if( numboxes * 2 <= desired_colors ) {
      b1 = find_biggest_color_pop( boxlist, numboxes );
    } else {
      b1 = find_biggest_volume( boxlist, numboxes );
    }
    if( b1 == NULL )		/* no splittable boxes left! */
    { break; }
    b2 = &boxlist[numboxes];	/* where new box will go */
    /* Copy the color bounds to the new box. */
    b2->c0max = b1->c0max;
    b2->c1max = b1->c1max;
    b2->c2max = b1->c2max;
    b2->c0min = b1->c0min;
    b2->c1min = b1->c1min;
    b2->c2min = b1->c2min;
    /* Choose which axis to split the box on.
       Current algorithm: longest scaled axis.
       See notes in update_box about scaling distances.
    */
    c0 = ( ( b1->c0max - b1->c0min ) << C0_SHIFT ) * C0_SCALE;
    c1 = ( ( b1->c1max - b1->c1min ) << C1_SHIFT ) * C1_SCALE;
    c2 = ( ( b1->c2max - b1->c2min ) << C2_SHIFT ) * C2_SCALE;
    /* We want to break any ties in favor of green, then red, blue last.
       This code does the right thing for R,G,B or B,G,R color orders only.
    */
    #if RGB_RED == 0
    cmax = c1;
    n = 1;
    if( c0 > cmax ) {
      cmax = c0;
      n = 0;
    }
    if( c2 > cmax ) {
      n = 2;
    }
    #else
    cmax = c1;
    n = 1;
    if( c2 > cmax ) {
      cmax = c2;
      n = 2;
    }
    if( c0 > cmax ) {
      n = 0;
    }
    #endif
    /* Choose split point along selected axis, and update box bounds.
       Current algorithm: split at halfway point.
       (Since the box has been shrunk to minimum volume,
       any split will produce two nonempty subboxes.)
       Note that lb value is max for lower box, so must be < old max.
    */
    switch( n ) {
      case 0:
        lb = ( b1->c0max + b1->c0min ) / 2;
        b1->c0max = lb;
        b2->c0min = lb + 1;
        break;
      case 1:
        lb = ( b1->c1max + b1->c1min ) / 2;
        b1->c1max = lb;
        b2->c1min = lb + 1;
        break;
      case 2:
        lb = ( b1->c2max + b1->c2min ) / 2;
        b1->c2max = lb;
        b2->c2min = lb + 1;
        break;
    }
    /* Update stats for boxes */
    update_box( cinfo, b1 );
    update_box( cinfo, b2 );
    numboxes++;
  }
  return numboxes;
}

static void compute_color( j_decompress_ptr cinfo, boxptr boxp, int icolor )
/* Compute representative color for a box, put it in colormap[icolor] */
{
  /* Current algorithm: mean weighted by pixels (not colors) */
  /* Note it is important to get the rounding correct! */
  my_cquantize_ptr cquantize = ( my_cquantize_ptr ) cinfo->cquantize;
  hist3d histogram = cquantize->histogram;
  histptr histp;
  int c0, c1, c2;
  int c0min, c0max, c1min, c1max, c2min, c2max;
  long count;
  long total = 0;
  long c0total = 0;
  long c1total = 0;
  long c2total = 0;
  c0min = boxp->c0min;
  c0max = boxp->c0max;
  c1min = boxp->c1min;
  c1max = boxp->c1max;
  c2min = boxp->c2min;
  c2max = boxp->c2max;
  for( c0 = c0min; c0 <= c0max; c0++ )
    for( c1 = c1min; c1 <= c1max; c1++ ) {
      histp = & histogram[c0][c1][c2min];
      for( c2 = c2min; c2 <= c2max; c2++ ) {
        if( ( count = *histp++ ) != 0 ) {
          total += count;
          c0total += ( ( c0 << C0_SHIFT ) + ( ( 1 << C0_SHIFT ) >> 1 ) ) * count;
          c1total += ( ( c1 << C1_SHIFT ) + ( ( 1 << C1_SHIFT ) >> 1 ) ) * count;
          c2total += ( ( c2 << C2_SHIFT ) + ( ( 1 << C2_SHIFT ) >> 1 ) ) * count;
        }
      }
    }
  cinfo->colormap[0][icolor] = ( JSAMPLE )( ( c0total + ( total >> 1 ) ) / total );
  cinfo->colormap[1][icolor] = ( JSAMPLE )( ( c1total + ( total >> 1 ) ) / total );
  cinfo->colormap[2][icolor] = ( JSAMPLE )( ( c2total + ( total >> 1 ) ) / total );
}

static void select_colors( j_decompress_ptr cinfo, int desired_colors )
/* Master routine for color selection */
{
  boxptr boxlist;
  int numboxes;
  int i;
  /* Allocate workspace for box list */
  boxlist = ( boxptr )( *cinfo->mem->alloc_small )
            ( ( j_common_ptr ) cinfo, JPOOL_IMAGE, desired_colors * SIZEOF( box ) );
  /* Initialize one box containing whole space */
  numboxes = 1;
  boxlist[0].c0min = 0;
  boxlist[0].c0max = MAXJSAMPLE >> C0_SHIFT;
  boxlist[0].c1min = 0;
  boxlist[0].c1max = MAXJSAMPLE >> C1_SHIFT;
  boxlist[0].c2min = 0;
  boxlist[0].c2max = MAXJSAMPLE >> C2_SHIFT;
  /* Shrink it to actually-used volume and set its statistics */
  update_box( cinfo, & boxlist[0] );
  /* Perform median-cut to produce final box list */
  numboxes = median_cut( cinfo, boxlist, numboxes, desired_colors );
  /* Compute the representative color for each box, fill colormap */
  for( i = 0; i < numboxes; i++ )
  { compute_color( cinfo, & boxlist[i], i ); }
  cinfo->actual_number_of_colors = numboxes;
  TRACEMS1( cinfo, 1, JTRC_QUANT_SELECTED, numboxes );
}

#define BOX_C0_LOG  (HIST_C0_BITS-3)
#define BOX_C1_LOG  (HIST_C1_BITS-3)
#define BOX_C2_LOG  (HIST_C2_BITS-3)

#define BOX_C0_ELEMS  (1<<BOX_C0_LOG) /* # of hist cells in update box */
#define BOX_C1_ELEMS  (1<<BOX_C1_LOG)
#define BOX_C2_ELEMS  (1<<BOX_C2_LOG)

#define BOX_C0_SHIFT  (C0_SHIFT + BOX_C0_LOG)
#define BOX_C1_SHIFT  (C1_SHIFT + BOX_C1_LOG)
#define BOX_C2_SHIFT  (C2_SHIFT + BOX_C2_LOG)


static int find_nearby_colors( j_decompress_ptr cinfo, int minc0, int minc1, int minc2,
                               JSAMPLE colorlist[] ) {
  int numcolors = cinfo->actual_number_of_colors;
  int maxc0, maxc1, maxc2;
  int centerc0, centerc1, centerc2;
  int i, x, ncolors;
  JPEG_INT32 minmaxdist, min_dist, max_dist, tdist;
  JPEG_INT32 mindist[MAXNUMCOLORS];	/* min distance to colormap entry i */
  maxc0 = minc0 + ( ( 1 << BOX_C0_SHIFT ) - ( 1 << C0_SHIFT ) );
  centerc0 = ( minc0 + maxc0 ) >> 1;
  maxc1 = minc1 + ( ( 1 << BOX_C1_SHIFT ) - ( 1 << C1_SHIFT ) );
  centerc1 = ( minc1 + maxc1 ) >> 1;
  maxc2 = minc2 + ( ( 1 << BOX_C2_SHIFT ) - ( 1 << C2_SHIFT ) );
  centerc2 = ( minc2 + maxc2 ) >> 1;
  minmaxdist = 0x7FFFFFFFL;
  for( i = 0; i < numcolors; i++ ) {
    /* We compute the squared-c0-distance term, then add in the other two. */
    x = GETJSAMPLE( cinfo->colormap[0][i] );
    if( x < minc0 ) {
      tdist = ( x - minc0 ) * C0_SCALE;
      min_dist = tdist * tdist;
      tdist = ( x - maxc0 ) * C0_SCALE;
      max_dist = tdist * tdist;
    } else if( x > maxc0 ) {
      tdist = ( x - maxc0 ) * C0_SCALE;
      min_dist = tdist * tdist;
      tdist = ( x - minc0 ) * C0_SCALE;
      max_dist = tdist * tdist;
    } else {
      /* within cell range so no contribution to min_dist */
      min_dist = 0;
      if( x <= centerc0 ) {
        tdist = ( x - maxc0 ) * C0_SCALE;
        max_dist = tdist * tdist;
      } else {
        tdist = ( x - minc0 ) * C0_SCALE;
        max_dist = tdist * tdist;
      }
    }
    x = GETJSAMPLE( cinfo->colormap[1][i] );
    if( x < minc1 ) {
      tdist = ( x - minc1 ) * C1_SCALE;
      min_dist += tdist * tdist;
      tdist = ( x - maxc1 ) * C1_SCALE;
      max_dist += tdist * tdist;
    } else if( x > maxc1 ) {
      tdist = ( x - maxc1 ) * C1_SCALE;
      min_dist += tdist * tdist;
      tdist = ( x - minc1 ) * C1_SCALE;
      max_dist += tdist * tdist;
    } else {
      /* within cell range so no contribution to min_dist */
      if( x <= centerc1 ) {
        tdist = ( x - maxc1 ) * C1_SCALE;
        max_dist += tdist * tdist;
      } else {
        tdist = ( x - minc1 ) * C1_SCALE;
        max_dist += tdist * tdist;
      }
    }
    x = GETJSAMPLE( cinfo->colormap[2][i] );
    if( x < minc2 ) {
      tdist = ( x - minc2 ) * C2_SCALE;
      min_dist += tdist * tdist;
      tdist = ( x - maxc2 ) * C2_SCALE;
      max_dist += tdist * tdist;
    } else if( x > maxc2 ) {
      tdist = ( x - maxc2 ) * C2_SCALE;
      min_dist += tdist * tdist;
      tdist = ( x - minc2 ) * C2_SCALE;
      max_dist += tdist * tdist;
    } else {
      /* within cell range so no contribution to min_dist */
      if( x <= centerc2 ) {
        tdist = ( x - maxc2 ) * C2_SCALE;
        max_dist += tdist * tdist;
      } else {
        tdist = ( x - minc2 ) * C2_SCALE;
        max_dist += tdist * tdist;
      }
    }
    mindist[i] = min_dist;	/* save away the results */
    if( max_dist < minmaxdist )
    { minmaxdist = max_dist; }
  }
  ncolors = 0;
  for( i = 0; i < numcolors; i++ ) {
    if( mindist[i] <= minmaxdist )
    { colorlist[ncolors++] = ( JSAMPLE ) i; }
  }
  return ncolors;
}


static void find_best_colors( j_decompress_ptr cinfo, int minc0, int minc1, int minc2,
                              int numcolors, JSAMPLE colorlist[], JSAMPLE bestcolor[] ) {
  int ic0, ic1, ic2;
  int i, icolor;
  register JPEG_INT32 * bptr;	/* pointer into bestdist[] array */
  JSAMPLE * cptr;		/* pointer into bestcolor[] array */
  JPEG_INT32 dist0, dist1;		/* initial distance values */
  register JPEG_INT32 dist2;		/* current distance in inner loop */
  JPEG_INT32 xx0, xx1;		/* distance increments */
  register JPEG_INT32 xx2;
  JPEG_INT32 inc0, inc1, inc2;	/* initial values for increments */
  /* This array holds the distance to the nearest-so-far color for each cell */
  JPEG_INT32 bestdist[BOX_C0_ELEMS * BOX_C1_ELEMS * BOX_C2_ELEMS];
  /* Initialize best-distance for each cell of the update box */
  bptr = bestdist;
  for( i = BOX_C0_ELEMS * BOX_C1_ELEMS * BOX_C2_ELEMS - 1; i >= 0; i-- )
  { *bptr++ = 0x7FFFFFFFL; }
  /* For each color selected by find_nearby_colors,
     compute its distance to the center of each cell in the box.
     If that's less than best-so-far, update best distance and color number.
  */
  /* Nominal steps between cell centers ("x" in Thomas article) */
#define STEP_C0  ((1 << C0_SHIFT) * C0_SCALE)
#define STEP_C1  ((1 << C1_SHIFT) * C1_SCALE)
#define STEP_C2  ((1 << C2_SHIFT) * C2_SCALE)
  for( i = 0; i < numcolors; i++ ) {
    icolor = GETJSAMPLE( colorlist[i] );
    /* Compute (square of) distance from minc0/c1/c2 to this color */
    inc0 = ( minc0 - GETJSAMPLE( cinfo->colormap[0][icolor] ) ) * C0_SCALE;
    dist0 = inc0 * inc0;
    inc1 = ( minc1 - GETJSAMPLE( cinfo->colormap[1][icolor] ) ) * C1_SCALE;
    dist0 += inc1 * inc1;
    inc2 = ( minc2 - GETJSAMPLE( cinfo->colormap[2][icolor] ) ) * C2_SCALE;
    dist0 += inc2 * inc2;
    /* Form the initial difference increments */
    inc0 = inc0 * ( 2 * STEP_C0 ) + STEP_C0 * STEP_C0;
    inc1 = inc1 * ( 2 * STEP_C1 ) + STEP_C1 * STEP_C1;
    inc2 = inc2 * ( 2 * STEP_C2 ) + STEP_C2 * STEP_C2;
    /* Now loop over all cells in box, updating distance per Thomas method */
    bptr = bestdist;
    cptr = bestcolor;
    xx0 = inc0;
    for( ic0 = BOX_C0_ELEMS - 1; ic0 >= 0; ic0-- ) {
      dist1 = dist0;
      xx1 = inc1;
      for( ic1 = BOX_C1_ELEMS - 1; ic1 >= 0; ic1-- ) {
        dist2 = dist1;
        xx2 = inc2;
        for( ic2 = BOX_C2_ELEMS - 1; ic2 >= 0; ic2-- ) {
          if( dist2 < *bptr ) {
            *bptr = dist2;
            *cptr = ( JSAMPLE ) icolor;
          }
          dist2 += xx2;
          xx2 += 2 * STEP_C2 * STEP_C2;
          bptr++;
          cptr++;
        }
        dist1 += xx1;
        xx1 += 2 * STEP_C1 * STEP_C1;
      }
      dist0 += xx0;
      xx0 += 2 * STEP_C0 * STEP_C0;
    }
  }
}


static void fill_inverse_cmap( j_decompress_ptr cinfo, int c0, int c1, int c2 )
/* Fill the inverse-colormap entries in the update box that contains */
/* histogram cell c0/c1/c2.  (Only that one cell MUST be filled, but */
/* we can fill as many others as we wish.) */
{
  my_cquantize_ptr cquantize = ( my_cquantize_ptr ) cinfo->cquantize;
  hist3d histogram = cquantize->histogram;
  int minc0, minc1, minc2;	/* lower left corner of update box */
  int ic0, ic1, ic2;
  register JSAMPLE * cptr;	/* pointer into bestcolor[] array */
  register histptr cachep;	/* pointer into main cache array */
  /* This array lists the candidate colormap indexes. */
  JSAMPLE colorlist[MAXNUMCOLORS];
  int numcolors;		/* number of candidate colors */
  /* This array holds the actually closest colormap index for each cell. */
  JSAMPLE bestcolor[BOX_C0_ELEMS * BOX_C1_ELEMS * BOX_C2_ELEMS];
  /* Convert cell coordinates to update box ID */
  c0 >>= BOX_C0_LOG;
  c1 >>= BOX_C1_LOG;
  c2 >>= BOX_C2_LOG;
  /* Compute true coordinates of update box's origin corner.
     Actually we compute the coordinates of the center of the corner
     histogram cell, which are the lower bounds of the volume we care about.
  */
  minc0 = ( c0 << BOX_C0_SHIFT ) + ( ( 1 << C0_SHIFT ) >> 1 );
  minc1 = ( c1 << BOX_C1_SHIFT ) + ( ( 1 << C1_SHIFT ) >> 1 );
  minc2 = ( c2 << BOX_C2_SHIFT ) + ( ( 1 << C2_SHIFT ) >> 1 );
  /* Determine which colormap entries are close enough to be candidates
     for the nearest entry to some cell in the update box.
  */
  numcolors = find_nearby_colors( cinfo, minc0, minc1, minc2, colorlist );
  /* Determine the actually nearest colors. */
  find_best_colors( cinfo, minc0, minc1, minc2, numcolors, colorlist,
                    bestcolor );
  /* Save the best color numbers (plus 1) in the main cache array */
  c0 <<= BOX_C0_LOG;		/* convert ID back to base cell indexes */
  c1 <<= BOX_C1_LOG;
  c2 <<= BOX_C2_LOG;
  cptr = bestcolor;
  for( ic0 = 0; ic0 < BOX_C0_ELEMS; ic0++ ) {
    for( ic1 = 0; ic1 < BOX_C1_ELEMS; ic1++ ) {
      cachep = & histogram[c0 + ic0][c1 + ic1][c2];
      for( ic2 = 0; ic2 < BOX_C2_ELEMS; ic2++ ) {
        *cachep++ = ( histcell )( GETJSAMPLE( *cptr++ ) + 1 );
      }
    }
  }
}


/*
   Map some rows of pixels to the output colormapped representation.
*/

METHODDEF( void )
pass2_no_dither( j_decompress_ptr cinfo,
                 JSAMPARRAY input_buf, JSAMPARRAY output_buf, int num_rows )
/* This version performs no dithering */
{
  my_cquantize_ptr cquantize = ( my_cquantize_ptr ) cinfo->cquantize;
  hist3d histogram = cquantize->histogram;
  register JSAMPROW inptr, outptr;
  register histptr cachep;
  register int c0, c1, c2;
  int row;
  JDIMENSION col;
  JDIMENSION width = cinfo->output_width;
  for( row = 0; row < num_rows; row++ ) {
    inptr = input_buf[row];
    outptr = output_buf[row];
    for( col = width; col > 0; col-- ) {
      /* get pixel value and index into the cache */
      c0 = GETJSAMPLE( *inptr++ ) >> C0_SHIFT;
      c1 = GETJSAMPLE( *inptr++ ) >> C1_SHIFT;
      c2 = GETJSAMPLE( *inptr++ ) >> C2_SHIFT;
      cachep = & histogram[c0][c1][c2];
      /* If we have not seen this color before, find nearest colormap entry */
      /* and update the cache */
      if( *cachep == 0 )
      { fill_inverse_cmap( cinfo, c0, c1, c2 ); }
      /* Now emit the colormap index for this cell */
      *outptr++ = ( JSAMPLE )( *cachep - 1 );
    }
  }
}


METHODDEF( void )
pass2_fs_dither( j_decompress_ptr cinfo,
                 JSAMPARRAY input_buf, JSAMPARRAY output_buf, int num_rows )
/* This version performs Floyd-Steinberg dithering */
{
  my_cquantize_ptr cquantize = ( my_cquantize_ptr ) cinfo->cquantize;
  hist3d histogram = cquantize->histogram;
  register LOCFSERROR cur0, cur1, cur2;	/* current error or pixel value */
  LOCFSERROR belowerr0, belowerr1, belowerr2; /* error for pixel below cur */
  LOCFSERROR bpreverr0, bpreverr1, bpreverr2; /* error for below/prev col */
  register FSERRPTR errorptr;	/* => fserrors[] at column before current */
  JSAMPROW inptr;		/* => current input pixel */
  JSAMPROW outptr;		/* => current output pixel */
  histptr cachep;
  int dir;			/* +1 or -1 depending on direction */
  int dir3;			/* 3*dir, for advancing inptr & errorptr */
  int row;
  JDIMENSION col;
  JDIMENSION width = cinfo->output_width;
  JSAMPLE *range_limit = cinfo->sample_range_limit;
  int *error_limit = cquantize->error_limiter;
  JSAMPROW colormap0 = cinfo->colormap[0];
  JSAMPROW colormap1 = cinfo->colormap[1];
  JSAMPROW colormap2 = cinfo->colormap[2];
  SHIFT_TEMPS
  for( row = 0; row < num_rows; row++ ) {
    inptr = input_buf[row];
    outptr = output_buf[row];
    if( cquantize->on_odd_row ) {
      /* work right to left in this row */
      inptr += ( width - 1 ) * 3;	/* so point to rightmost pixel */
      outptr += width - 1;
      dir = -1;
      dir3 = -3;
      errorptr = cquantize->fserrors + ( width + 1 ) * 3; /* => entry after last column */
      cquantize->on_odd_row = FALSE; /* flip for next time */
    } else {
      /* work left to right in this row */
      dir = 1;
      dir3 = 3;
      errorptr = cquantize->fserrors; /* => entry before first real column */
      cquantize->on_odd_row = TRUE; /* flip for next time */
    }
    /* Preset error values: no error propagated to first pixel from left */
    cur0 = cur1 = cur2 = 0;
    /* and no error propagated to row below yet */
    belowerr0 = belowerr1 = belowerr2 = 0;
    bpreverr0 = bpreverr1 = bpreverr2 = 0;
    for( col = width; col > 0; col-- ) {
      /* curN holds the error propagated from the previous pixel on the
         current line.  Add the error propagated from the previous line
         to form the complete error correction term for this pixel, and
         round the error term (which is expressed * 16) to an integer.
         RIGHT_SHIFT rounds towards minus infinity, so adding 8 is correct
         for either sign of the error value.
         Note: errorptr points to *previous* column's array entry.
      */
      cur0 = RIGHT_SHIFT( cur0 + errorptr[dir3 + 0] + 8, 4 );
      cur1 = RIGHT_SHIFT( cur1 + errorptr[dir3 + 1] + 8, 4 );
      cur2 = RIGHT_SHIFT( cur2 + errorptr[dir3 + 2] + 8, 4 );
      /* Limit the error using transfer function set by init_error_limit.
         See comments with init_error_limit for rationale.
      */
      cur0 = error_limit[cur0];
      cur1 = error_limit[cur1];
      cur2 = error_limit[cur2];
      /* Form pixel value + error, and range-limit to 0..MAXJSAMPLE.
         The maximum error is +- MAXJSAMPLE (or less with error limiting);
         this sets the required size of the range_limit array.
      */
      cur0 += GETJSAMPLE( inptr[0] );
      cur1 += GETJSAMPLE( inptr[1] );
      cur2 += GETJSAMPLE( inptr[2] );
      cur0 = GETJSAMPLE( range_limit[cur0] );
      cur1 = GETJSAMPLE( range_limit[cur1] );
      cur2 = GETJSAMPLE( range_limit[cur2] );
      /* Index into the cache with adjusted pixel value */
      cachep = & histogram[cur0 >> C0_SHIFT][cur1 >> C1_SHIFT][cur2 >> C2_SHIFT];
      /* If we have not seen this color before, find nearest colormap */
      /* entry and update the cache */
      if( *cachep == 0 )
      { fill_inverse_cmap( cinfo, cur0 >> C0_SHIFT, cur1 >> C1_SHIFT, cur2 >> C2_SHIFT ); }
      /* Now emit the colormap index for this cell */
      {
        register int pixcode = *cachep - 1;
        *outptr = ( JSAMPLE ) pixcode;
        /* Compute representation error for this pixel */
        cur0 -= GETJSAMPLE( colormap0[pixcode] );
        cur1 -= GETJSAMPLE( colormap1[pixcode] );
        cur2 -= GETJSAMPLE( colormap2[pixcode] );
      }
      /* Compute error fractions to be propagated to adjacent pixels.
         Add these into the running sums, and simultaneously shift the
         next-line error sums left by 1 column.
      */
      {
        register LOCFSERROR bnexterr, delta;
        bnexterr = cur0;	/* Process component 0 */
        delta = cur0 * 2;
        cur0 += delta;		/* form error * 3 */
        errorptr[0] = ( FSERROR )( bpreverr0 + cur0 );
        cur0 += delta;		/* form error * 5 */
        bpreverr0 = belowerr0 + cur0;
        belowerr0 = bnexterr;
        cur0 += delta;		/* form error * 7 */
        bnexterr = cur1;	/* Process component 1 */
        delta = cur1 * 2;
        cur1 += delta;		/* form error * 3 */
        errorptr[1] = ( FSERROR )( bpreverr1 + cur1 );
        cur1 += delta;		/* form error * 5 */
        bpreverr1 = belowerr1 + cur1;
        belowerr1 = bnexterr;
        cur1 += delta;		/* form error * 7 */
        bnexterr = cur2;	/* Process component 2 */
        delta = cur2 * 2;
        cur2 += delta;		/* form error * 3 */
        errorptr[2] = ( FSERROR )( bpreverr2 + cur2 );
        cur2 += delta;		/* form error * 5 */
        bpreverr2 = belowerr2 + cur2;
        belowerr2 = bnexterr;
        cur2 += delta;		/* form error * 7 */
      }
      /* At this point curN contains the 7/16 error value to be propagated
         to the next pixel on the current line, and all the errors for the
         next line have been shifted over.  We are therefore ready to move on.
      */
      inptr += dir3;		/* Advance pixel pointers to next column */
      outptr += dir;
      errorptr += dir3;		/* advance errorptr to current column */
    }
    /* Post-loop cleanup: we must unload the final error values into the
       final fserrors[] entry.  Note we need not unload belowerrN because
       it is for the dummy column before or after the actual array.
    */
    errorptr[0] = ( FSERROR ) bpreverr0; /* unload prev errs into array */
    errorptr[1] = ( FSERROR ) bpreverr1;
    errorptr[2] = ( FSERROR ) bpreverr2;
  }
}

static void init_error_limit( j_decompress_ptr cinfo )
/* Allocate and fill in the error_limiter table */
{
  my_cquantize_ptr cquantize = ( my_cquantize_ptr ) cinfo->cquantize;
  int * table;
  int in, out;
  table = ( int * )( *cinfo->mem->alloc_small )
          ( ( j_common_ptr ) cinfo, JPOOL_IMAGE, ( MAXJSAMPLE * 2 + 1 ) * SIZEOF( int ) );
  table += MAXJSAMPLE;		/* so can index -MAXJSAMPLE .. +MAXJSAMPLE */
  cquantize->error_limiter = table;
#define STEPSIZE ((MAXJSAMPLE+1)/16)
  /* Map errors 1:1 up to +- MAXJSAMPLE/16 */
  out = 0;
  for( in = 0; in < STEPSIZE; in++, out++ ) {
    table[in] = out;
    table[-in] = -out;
  }
  /* Map errors 1:2 up to +- 3*MAXJSAMPLE/16 */
  for( ; in < STEPSIZE * 3; in++, out += ( in & 1 ) ? 0 : 1 ) {
    table[in] = out;
    table[-in] = -out;
  }
  /* Clamp the rest to final out value (which is (MAXJSAMPLE+1)/8) */
  for( ; in <= MAXJSAMPLE; in++ ) {
    table[in] = out;
    table[-in] = -out;
  }
#undef STEPSIZE
}

METHODDEF( void )
finish_pass1( j_decompress_ptr cinfo ) {
  my_cquantize_ptr cquantize = ( my_cquantize_ptr ) cinfo->cquantize;
  /* Select the representative colors and fill in cinfo->colormap */
  cinfo->colormap = cquantize->sv_colormap;
  select_colors( cinfo, cquantize->desired );
  /* Force next pass to zero the color index table */
  cquantize->needs_zeroed = TRUE;
}


METHODDEF( void )
finish_pass2( j_decompress_ptr cinfo ) {
}


METHODDEF( void )
start_pass_2_quant( j_decompress_ptr cinfo, wxjpeg_boolean is_pre_scan ) {
  my_cquantize_ptr cquantize = ( my_cquantize_ptr ) cinfo->cquantize;
  hist3d histogram = cquantize->histogram;
  int i;
  if( cinfo->dither_mode != JDITHER_NONE )
  { cinfo->dither_mode = JDITHER_FS; }
  if( is_pre_scan ) {
    /* Set up method pointers */
    cquantize->pub.color_quantize = prescan_quantize;
    cquantize->pub.finish_pass = finish_pass1;
    cquantize->needs_zeroed = TRUE; /* Always zero histogram */
  } else {
    /* Set up method pointers */
    if( cinfo->dither_mode == JDITHER_FS )
    { cquantize->pub.color_quantize = pass2_fs_dither; }
    else
    { cquantize->pub.color_quantize = pass2_no_dither; }
    cquantize->pub.finish_pass = finish_pass2;
    /* Make sure color count is acceptable */
    i = cinfo->actual_number_of_colors;
    if( i < 1 )
    { ERREXIT1( cinfo, JERR_QUANT_FEW_COLORS, 1 ); }
    if( i > MAXNUMCOLORS )
    { ERREXIT1( cinfo, JERR_QUANT_MANY_COLORS, MAXNUMCOLORS ); }
    if( cinfo->dither_mode == JDITHER_FS ) {
      size_t arraysize = ( size_t )( ( cinfo->output_width + 2 ) *
                                     ( 3 * SIZEOF( FSERROR ) ) );
      /* Allocate Floyd-Steinberg workspace if we didn't already. */
      if( cquantize->fserrors == NULL )
        cquantize->fserrors = ( FSERRPTR )( *cinfo->mem->alloc_large )
                              ( ( j_common_ptr ) cinfo, JPOOL_IMAGE, arraysize );
      /* Initialize the propagated errors to zero. */
      jzero_far( ( void FAR * ) cquantize->fserrors, arraysize );
      /* Make the error-limit table if we didn't already. */
      if( cquantize->error_limiter == NULL )
      { init_error_limit( cinfo ); }
      cquantize->on_odd_row = FALSE;
    }
  }
  /* Zero the histogram or inverse color map, if necessary */
  if( cquantize->needs_zeroed ) {
    for( i = 0; i < HIST_C0_ELEMS; i++ ) {
      jzero_far( ( void FAR * ) histogram[i],
                 HIST_C1_ELEMS * HIST_C2_ELEMS * SIZEOF( histcell ) );
    }
    cquantize->needs_zeroed = FALSE;
  }
}

METHODDEF( void )
new_color_map_2_quant( j_decompress_ptr cinfo ) {
  my_cquantize_ptr cquantize = ( my_cquantize_ptr ) cinfo->cquantize;
  /* Reset the inverse color map */
  cquantize->needs_zeroed = TRUE;
}

void jinit_2pass_quantizer( j_decompress_ptr cinfo ) {
  my_cquantize_ptr cquantize;
  int i;
  cquantize = ( my_cquantize_ptr )
              ( *cinfo->mem->alloc_small )( ( j_common_ptr ) cinfo, JPOOL_IMAGE,
                  SIZEOF( my_cquantizer ) );
  cinfo->cquantize = ( struct jpeg_color_quantizer * ) cquantize;
  cquantize->pub.start_pass = start_pass_2_quant;
  cquantize->pub.new_color_map = new_color_map_2_quant;
  cquantize->fserrors = NULL;	/* flag optional arrays not allocated */
  cquantize->error_limiter = NULL;
  /* Make sure jdmaster didn't give me a case I can't handle */
  if( cinfo->out_color_components != 3 )
  { ERREXIT( cinfo, JERR_NOTIMPL ); }
  /* Allocate the histogram/inverse colormap storage */
  cquantize->histogram = ( hist3d )( *cinfo->mem->alloc_small )
                         ( ( j_common_ptr ) cinfo, JPOOL_IMAGE, HIST_C0_ELEMS * SIZEOF( hist2d ) );
  for( i = 0; i < HIST_C0_ELEMS; i++ ) {
    cquantize->histogram[i] = ( hist2d )( *cinfo->mem->alloc_large )
                              ( ( j_common_ptr ) cinfo, JPOOL_IMAGE,
                                HIST_C1_ELEMS * HIST_C2_ELEMS * SIZEOF( histcell ) );
  }
  cquantize->needs_zeroed = TRUE; /* histogram is garbage now */
  /* Allocate storage for the completed colormap, if required.
     We do this now since it is FAR storage and may affect
     the memory manager's space calculations.
  */
  if( cinfo->enable_2pass_quant ) {
    /* Make sure color count is acceptable */
    int desired = cinfo->desired_number_of_colors;
    /* Lower bound on # of colors ... somewhat arbitrary as long as > 0 */
    if( desired < 8 )
    { ERREXIT1( cinfo, JERR_QUANT_FEW_COLORS, 8 ); }
    /* Make sure colormap indexes can be represented by JSAMPLEs */
    if( desired > MAXNUMCOLORS )
    { ERREXIT1( cinfo, JERR_QUANT_MANY_COLORS, MAXNUMCOLORS ); }
    cquantize->sv_colormap = ( *cinfo->mem->alloc_sarray )
                             ( ( j_common_ptr ) cinfo, JPOOL_IMAGE, ( JDIMENSION ) desired, ( JDIMENSION ) 3 );
    cquantize->desired = desired;
  } else
  { cquantize->sv_colormap = NULL; }
  /* Only F-S dithering or no dithering is supported. */
  /* If user asks for ordered dither, give him F-S. */
  if( cinfo->dither_mode != JDITHER_NONE )
  { cinfo->dither_mode = JDITHER_FS; }
  /* Allocate Floyd-Steinberg workspace if necessary.
     This isn't really needed until pass 2, but again it is FAR storage.
     Although we will cope with a later change in dither_mode,
     we do not promise to honor max_memory_to_use if dither_mode changes.
  */
  if( cinfo->dither_mode == JDITHER_FS ) {
    cquantize->fserrors = ( FSERRPTR )( *cinfo->mem->alloc_large )
                          ( ( j_common_ptr ) cinfo, JPOOL_IMAGE,
                            ( size_t )( ( cinfo->output_width + 2 ) * ( 3 * SIZEOF( FSERROR ) ) ) );
    /* Might as well create the error-limiting table too. */
    init_error_limit( cinfo );
  }
}

#endif /* QUANT_2PASS_SUPPORTED */
